1. Field of the Invention
The present invention relates to a technique for reducing image shake caused by hand shaking or the like when shooting photos.
2. Description of the Related Art
In recent years, there have been developed image shake correcting devices for correcting image shake caused by hand shaking or the like as image pickup apparatuses are made smaller in size. An image shake correction mechanism which is available for both still image shooting and moving image shooting while preventing an increase in the size of the image pickup apparatus suppresses image shake by shifting a part (correction member) of a lens system. A method for moving a correction lens within a plane perpendicular to the optical axis plane has become popular.
As a method for suppressing degradation in the optimal image forming performance while broadening an image shake correction angle, Japanese Patent No. 3003370 discloses a configuration in which a correction member is pivoted about a point on the optical axis. There has also been proposed a high level method for moving a lens system in a three-dimensional manner or changing the attitude of the lens system in respect to the position and attitude of the same. The method can suppress degradation in the optimal image forming performance relating to sharpness and blur even when a correction angle is broadened.
In recent years, with the rise of electronic correction and circuit techniques, so-called an electronic image shake correction function has been implemented for electronically correcting image distortion such as radial distortion or the like. When electronic image shake correction is used in combination with optical image shake correction, there have been proposed some measures for performing electronic correction by moving distortion image data or correction data in translation parallel to an optical center coordinate by monitoring the movement of the optical center coordinate on an image plane in concert with the movement of an optical image (see Japanese Patent Laid-Open No. 2012-231262).
When image shake is stopped by moving a correction member in a three-dimensional manner or changing the attitude thereof through image shake correction control in order to extend a range of correction, the effect of suppressing degradation in the optimal image forming performance relating to sharpness and blur is obtained. On the other hand, distortion characteristics are reduced, resulting in the occurrence of image distortion in which the shape of an image significantly and complexly varies due to the driving of the correction member. While design has conventionally been made so as to cause an image shift only to suppress the occurrence of eccentric distortion aberration as much as possible upon shifting a correction lens or the like, such image distortion occurs because the eccentric distortion aberration is tolerated in order to suppress sharpness and blur.
Phenomenon under the image shake correction control for image distortion correction is as follows:
(1) Handling of image distortion information and correction information about image distortion is complicated.
(2) Higher-order geometric deformation processing needs to be performed for image distortion correction.
(3) An increase in resources such as data storage capacity must be taken for achieving higher precision.
Firstly, a description will be given of (1). An optical system upon lens driving is a decentered system, and the adverse effect of image distortion at high image height needs to be quantitatively grasped with high precision in imaging system applications. Thus, it is difficult to quantitatively handle the adverse effect of image distortion by classifying image distortion into properties such as distortion aberration and eccentric aberration for correcting the adverse effect of image distortion by using a quantitation indicator obtained from an optical CAD (Computer-Aided Design) or actual measurement in accordance with the paraxial theory and aberration theory. More specifically, image distortion information and correction information about image distortion can only be acquired and measured, such that all the influences of various image distortion factors are included in the promiscuous form, by means of ray tracing with an optical CAD or measurement of the amount of movement of an ideal point on an actual chart under the adverse effect of image distortion.
With regard to (2), image distortion needs to be interpreted in a comprehensive manner, so that image distortion must be handled as distortion which nonlinearly varies in a spatially complex manner. Consequently, when an attempt is made to faithfully correct image distortion, a geometric transformation circuit which is capable of performing higher-order free deformation or approximated higher-order polynomial deformation is required.
With regard to (3), when an assumption is made to drive a lens in a correction angle range in two axes perpendicular to each other in, for example, the yaw direction and the pitch direction, correction information which occupies a large storage capacity must be held in the form of a two-dimensional geometric deformation amount vector map for each correction angle state. In addition, image distortion varies depending on camera parameters such as a zoom state, an aperture value, and an object distance, and thus, enormous amount of correction information needs to be held in a memory. For example, the improving effect is still limited by discretely holding correction information based on the assumption that correction angle interpolation processing is performed. Thus, when an assumption is made for implementing immediate processing or mounting in an installed apparatus, image distortion correction is not realistic.
With regard to the method for shifting a part of a lens system in a direction perpendicular to the optical axis, measures disclosed in Japanese Patent Laid-Open No. 2012-231262 are insufficient when an attempt is made to correct image distortion with higher precision. The reason for this is that, even when a part of a lens system is shifted in a direction perpendicular to the optical axis, the shape of image distortion varies in response to a lens driving by the adverse effect of the remaining eccentric distortion aberration in terms of the strict interpretation of image distortion. Faithfully handling image distortion without omitting such variation is the key to realize correction with high precision. With the recent advancement of an increase in the screen size and an improvement in high resolution of a display unit and an increase in the number of pixels in an image pickup apparatus itself, image distortion correction needs to be performed with high precision in a situation where a correction error cannot be ignored.